1. A does a work in 10 days and B does the same work in 15 days. In how many days they together will do the same work? (RRB, 2003)
a) 5 days b)6 days c)8 days d)9 days

2. A man can do a job in 15 days. His father takes 20 days and his son finishes it in 25 days. How long will they take to complete the job if they all work together?(Hotel Management, 2008)
a) Less than 6 days b) Exactly 6 days c) Approximately 6.4 days d) More than 10 days

3. A and B can do a piece of work in 8 days, B and C can do the same work in 12 days. A,B and C together can finish it in 6 days. A and C together will do it in: (RRB, 2007)
a) 4 days b)6 days c)8 days d)12 days

4. A works twice as fast as B. If B can complete a work 12 days independently, the number of days in which A and B can together finish the work is: (Asst. Grade 1997)
a) 4 days b)6 days c)8 days d)18 days

5. A is 50% efficient as B. C does half of the work done by A and B together. If C Alone can does the work in 40 days, then A,B and C can do the work in: (RRB, 2004)
a) 13 1/3 days b) 15 days c) 20 days d) 30 days

Ans: 1. (b) 2. (c) 3. (c) 4. (a) 5. (a)

Note: Main logic behind these problems is,

1. If A can do a piece of work in n days then A’s 1 day’s work = (1/n).
Example: If A can do a piece of work in 10 days then A’s one day’s work = (1/10).

2. If A’s one day’s work = 1/n, then A can finish the work in n days.
Example: If A’s one day’s work = 1/10, then A can finish the work in 10 days.

3. If A is thrice as good a workman as B, then :
Ratio of work done by A and B = 3 : 1.
Ratio of times taken by A and B to finish a work = 1 : 3.

Pattern 2

1. Sachin is younger than Rahul by 4 years. If their ages are in the respective ratio of 7 : 9 how old is sachin? (Bank PO, 2008)
a) 16 years b) 18 years c) 28 years d) Cannot be determined e) None of these

2. A man is 24 years older than his son. In two years, his age will be twice the age of his son. The present age of the son is: (RRB, 2007)
a) 14 years b) 18 years c) 20 years d) 22 years

3. Father is aged three times more than his son Ronit. After 8 years he would be two and a half times of Ronit’s age. After further 8 years, how many times would he be of Ronit’s age? (CBI, 2004)
a) 2 times b) 2 ½ times c) 2 ¾ times d) 3 times

4. A father said to his son, “I was as old as you are at present at the time of your birth”. If the father’s age is 38 years now, the son’s age 5 years back was: (Assist Grade, 2003)
a) 14 years b) 19 years c) 33 years d) 38 years

5. A person was asked to state his age in years. His reply was “Take my age three years hence, multiply it by 3 and then subtract three times my age three years ago and you will know how old I am.” What was age of that person? (SSC, 2004)
a) 18 years b) 20 years c) 24 years d) 32 years